Plant for drying moist materials



Sept: 11, 1934.

' PLANT 30R DRYING MOIST MATERIALS Filed June 9. 1931 S-Sheets Sheet 1 Eg -.5 Eye A! 4 X \27 lnvenfor.

RfscHuLwj'rz 1,

$6131:- 11, 1934. I SCHULWITZ 1,973,270

PLANT FOR DRYING MOIST MATERIALS Filed June 9, 1931 a sheets-sheet 2 I I I l I I I I I I I I I I I I I I l I I I I l K\ 4X? I 1. I 'I I \I/ I I I I I I P 1934. R. SCHULWITZ PLANT FOR DRYING MOIST MATERIALS 3 Sheets-Sheet Fil ed June 9. 1951 Patented Sept. 11, 1934 UNITED STATE FATE Application June 9, 1931, Serial No. 543,101 in Germany June 5, 1930 Claims.

My invention relates to drying plants, and more particularly to plants of the type in which a furnace and a pneumatic final drier are connected to a preliminary drier. 1

It is an object of my invention to so designs. drier of this type that overheating of the material is prevented and the efiiciency is a maximum.

To this end .I -provide means for conducting the gases from the furnace to the pneumatic final drier through the preliminary drier.

In the preliminary drier which may be of any suitable type, the gases give up a considerable percentage of their heat while flowing in indirect contact with the material so that in the final pneumatic drier in which the gases how in direct contact with the material, their temperature is so low that the material is not overheated. Loss of heat is avoided as the gases flow in the final drier and so the efficiency is a maximum.

Drying is particularly important for agricultural products as it conserves the nutritious properties much better than acidulation.

Many driers have already been suggested and driers of the pneumatic type in which the material is conveyed through long tubes by a flow of heating gas, and dried as it moves in the tubes,

have been preferred on account of their low weight, high output and consequently low initial cost, and their rapid operation. @n the other hand, they are not suitable for too moist material because the heat transfer to the material is poor if in this condition, and the high temperature may be harmful to the particles and deteriorate the digestibility of the albumens.

It has also been proposed to combine with a pneumatic final drier a preliminary drier from which the gases were conducted to a heat. ex-

changer for heating the cold air to the final drier.

' 5 tive temperature must be lower than in the pneumatic drier to prevent premature formation of films on the cells which would interfere with the discharge of the moisture. The troughs have double walls and the heating gases are in contact only with the outer wall, the clearance between the inner and outer walls acting as a heat insulator;

In order to reduce to a minimumthe overall size of the plant I may arrange the preliminary drier above the furnace, and the tubes of the final or pneumatic drier above the preliminary drier in horizontal position.

, The preliminary drier is preferably equipped with helical conveyers. As the volume of the material becomes less and less as it gets drier while the temperature in all troughs is constant, the velocity at which the material travels in the troughs, is reduced as the volume is reduced so that in all troughs the same amount of material per unit of time is conveyedand overheating of the partly dried material is prevented. i may reduce the rotational velocity of the helical conveyers with decreasing volume, or I may make the helix in each succeeding trough smaller than in the preceding one.

In order to prevent ejection of only partly dried material, I provide a classifier at the end of the final o1 pneumatic drier by which the material is selectively ejected or returned to the plant for finishing. I

If desired, cold air may be admitted to the pneumatic drier in order to regulate the temperature inthe several parts of the drier.

In the accompanying drawings two types of driers embodying my invention are illustrated diagrammatically by way of example.

In the drawings Fig. 1 is an elevation of a plant in which the intermediate and final driers are arranged at the rear of the furnace, and the tubes of the final drierare vertical,

Fig. 2 is a plan view of Fig. 1,

Fig. 3 is an elevation ,of a plant in which the preliminary and final driers are arranged on the furnace, with the tubes of the final drier in horizontal position,

Fig. 4 shows an air inlet valve in one of the tubes of the final drier,

Fig. 5 is an elevation, and

Fig. 6 is a plan view of "an agitator in one of the tubes,

Fig. 7 is a partly sectional elevation of one of the troughs in the preliminary drier, with its helix,

Fig.3 is an end elevation of the trough,

Fig. 9' shows a modified trough,

Figs. 10 and 11 illustrate two types of impellers in the knees of the tubes.

Referring now to the drawings, and first to Figs. 1 and 2, 1 is a furnace, 3, 3 are the troughs of the preliminary drier, each with a helix '7, and 2 is a flue connecting one end of the preliminary drier tothe furnace 1. The helixes '7 are operated atsuch a speed or their pitch is so determined that the velocity of the material steadily decreases, as and for the purpose specified. a is a rotary screen at the end of the-preliminary drier for the reception of the material which is sulficiently dry after passing through the pre: liminary drier. This is particularly the finer portion of the material. The finer material from the screen 8 is delivered to a discharge pipe, not shown, or to a conveyer 9, for further treatment.

11 and 12 are two vertical pipes of the final drier, l4 beingits third vertical pipe. Pipe 11 is connected to the furnace 1 by a flue 23, and is supplied with the coarser material from the screen 8 by a charging device 10. The material rises in the pipe 11 and descends in the pipe 12 until finally it is delivered to the base of the pipe 14 through a bend and by a charging device 13 which also entrains the material from the conveyer 9. The inside diameter of the third pipe 14 is larger than that of the'pipes 11, 12, and 15 is a fan exerting suction on the tube 14 at its upper end. 16 is an inertia separator between the tube 14 and the fan 15. The fine material which is dry, is conducted to a dust separator 1'7, 24 which delivers to a cooling conveyer 18.

The material may also be discharged directly at the lower end of the separator, and filled into bags. 20 is a chute at the lower end of the inertia separator 16 and 21 is a classifier screen to which the chute 20 delivers.

The screen 21, having a twofold layer of screening material, classes the dried material into three classes. Fine material is delivered to the cooling con-' veyer 18 to which air'is admitted for accelerating the cooling and drying of the material. The material of medium fineness is returned to the charging device, and the coarse material is returned to the first helix of the preliminary drier.

In order to reduce the temperature of the gas delivered totube 11, a slide 28 may be' provided for admitting cold air to the flue 23. The temperature of the gas admitted to tube 14 is reduced already by giving up a portion of its heat in the preliminary drier, but a valve 26, Fig. 4,

may be provided in this tube for regulating the temperature.

lwhirling wheels 27 may be arranged in the tubes 11, 12, and 14, or in any other position in order to agitate the gas in the tubes and to bring the material into contact with fresh molecules of gas. Wheels27 are shown to alarger scale in Figs. 5 and 6.

Referring to Fig. 3, the troughs 3 of the preliminary drier are here arranged above the furstufling boxes 31 at the joints, if desired, to that the members are free to expand.

Obviously, with a view to reducing the overall size of the plant, it is desirable that the bends or knees at the ends of the tubes should be of small radius while on theother hand the radius should be large "so that the material will flow freely. This difilculty is overcome by providing impellers in the bends or knees, as shown in Figs. 10 and 11. The impeller 32 may have the usual curved vanes 33, Fig 10, or bucket-shaped vanes 34, Fig. 11, in which latter casethe material is conveyed by suction and pressure. 4

I claim: 1

1. A device for drying moist materials, comprising an indirectly heated drier in which the material is preheated and pre-dried, a second and a final drier consisting each of a pneumatic piping, and a classifier for sorting the material coming out of the final drier, ejecting the dried portions thereof and distributing the still moist portions to the respective driers according to their degree of dryness.

2. A device according to claim 1 in which the preliminary drier comprises troughs, an extensible outer wall for each trough, a free air space being formed between each trough and outer wall, screw-conveyors for conveying the material to bedried through said troughs, a drive for said conveyors; and a furnace whose heating gases are passed alongthe outside of said outer wall and deliver part of their heat indirectly to the conveyed material.

' 3. In a device according to claim 1 a threepart rotary screen connecting'with the sorting device of the final drier and classifying the material three-fold, a discharge device connected to a part of the screen for removing perfectly dried material, a second discharge device connecting another part of the screen with the inlet of the final drier for returning thereto material not per-' fectly dried, and a thirddischarge device connecting the third part of the screen with the second drier for returning thereto the remainder of the material. I

4. A device according to claim 1, in which the preliminary drier is formed of a horizontal chamher and the pneumatic conveying pipes of the second and final driers are horizontally disposed on said chamber side by side.

5. In a device according to claim 1, vane wheels arranged atthe bends of the conveying pipes for passing the material from one pipe into the next one.

- RICHARD SCHULWITZ. 

